This invention relates to a hydraulic operating apparatus wherein a piston in a cylinder is actuated by a fluid under high pressure and, more particularly, to a hydraulic operating apparatus wherein the action of the fluid under high pressure exerted on a pressure receiving surface of the piston on the opposite side of a piston rod is improved.
In hydraulic operating apparatus known in the art, a fluid under high pressure is applied at all times to a pressure receiving surface of the piston of an actuating cylinder on the side of the piston rod, and a control valve associated with the actuating cylinder is actuated to apply the fluid under high pressure to the pressure receiving surface of the piston on the opposite side of the piston rod to thereby produce a pressure differential commensurate with the difference in area between the two pressure receiving surfaces, so as to move the piston by the pressure differential in a direction in which the piston rod extends from the piston. Also, the piston is moved at high speed in a direction opposite the direction in which the piston rod extends from the piston by discharging the fluid existent on the opposite side of the piston rod.
This type of hydraulic operating apparatus is used as a driving unit such as used with an emergency circuit breaker for an electric power system which unit is required to have high speed operation.
Some disadvantages are associated with prior hydraulic operating apparatus. Conventional hydraulic operating apparatus have to fulfill several requirements. One of such requirements is that sealing must be maintained over a prolonged period of time to the control valve for admitting a fluid under high pressure to the portion of the actuating cylinder on the side of the piston opposite the piston rod and discharging same therefrom, to avoid leakage of the fluid under high pressure to a low pressure tank which should act on the side of the piston opposite the piston rod. Another requirement is that a seal must be provided over a prolonged period of time to the control valve to prevent the fluid under high pressure from acting on the pressure receiving surface of the piston on the side thereof opposite the piston rod, so as to maintain the piston in a position in which it is located at the end of the actuating cylinder on the side of the piston opposite the piston rod. The need to meet all of these requirements renders the construction of the control valve complex, thereby raising the problem that difficulties are experienced in providing a satisfactory seal to the control valve. As a result, the provision of a satisfactory seal to the control valve to keep its performance at a high level in actual use entails a very high degree of precision finishes and hence an increase in production cost.